Modbus USB PORTNOTOPENERROR

dear All

I using node-red to convert a Modbus signal to MQTT .
It was working fine. However I have install on my raspberry Pi4 a SSH and VNC connection in order to have a distance access. I do not know if it is linking but now , node-red said me that :

"Error: {"name":"PortNotOpenError","message":"Port Not Open","errno":"ECONNREFUSED"}"

I am using the " /dev/ttyUSB0" designation .

I have seach hours on forum and internet but didn't find an easy answer about this permission needed.

could you help ?

regards

Beber